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I am using the latest version of LyX and I am having trouble getting the limits to work at all. Ideally, I'd like to be able to place the summation limits above and below the sigma. However, at this point, I would settle for the less-pleasing-to-my-eyes variant of having the limits in the northeast and southeast corners of the symbol. However, try as I might, LyX does not want to place the limits anywhere. The "Change Limits Type" whose use I have seen recommended in various forums remains greyed out no matter what I do and the documentation does not provide any information I have yet found on how the process is even supposed to work in theory. On an admittedly editorial note, I am beginning to feel LyX is extremely lacking in documentation, which is unfortunate as I think it otherwise is a great application. Anyway, if Someone could point me in the direction of how to resolve this issue, I'd greatly appreciate it.

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The problem might be that you first have to type at least one of lower or upper limit, or need to place the cursor at the \sum symbol to be able to change the limit type.

  1. "Insert > Math > Display Formula" (Crtl+Shift+M).
  2. Type \sum, hit space.
  3. Type _ as used for indices in math mode and type the lower limit (for example "i=1"), hit space.
  4. Type ^ as used for exponents in math mode and type the upper limit (for example "10"), hit space.

There is some documentation, which is integrated in LyX. You can find basic information about math mode in "Help > Tutorial" in Chapter 4 "Using Math" and advanced information in "Help > Math" in Chapter 10 "Operators".

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up vote 3 down vote accepted

I found the answer. With the cursor just to the right of the summation symbol, click the "subscript" button to place the beginning of the limit below the sigma. With the cursor just to the right of the sigma, click the "superscript" button to place the end of the limit just above the sigma.

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This does not work for inline formulas, you need to use Display Formula as e-birk suggests. What did you try in the first place and didn't work? – kon psych Jul 24 '14 at 21:29
You can also press the underscore key "_" fur subscript and the exponent key "^" for superscript. As mentioned in the answer below. – Paul Rougieux May 10 at 9:17

With the commands \overset↓ and \underset↓ characters can be placed above or below an operator, respectively, to accent it

source: http://elyxer.nongnu.org/lyx/Math.html [section 7.2]

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Welcome to TeX.SX! – Heiko Oberdiek Apr 6 '14 at 9:10

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